What are lysosomes: the structure, composition and functions of lysosomes

How can a cell "digest" substances that enter the cytoplasm? The answer can be obtained by considering what a lysosome is. What is their structure? Due to what properties are these organelles capable of performing their function?

Lysosomes. Features of structure and function

Lysosome is an organoid of a cell about 0.2 μm in size, surrounded by a single membrane and containing hydrolytic enzymes. The main function of such vesicles is the cleavage of substances that enter the cell through endocytosis, or their own molecules, in which there is no longer any need.

What is the lysosome in terms of structure?

Splitting, or degradation of substances, is carried out with the help of hydrolases - enzymes capable of working in an acidic environment. In order to maintain a low pH, vacuolar type ATPases (V-type) are built into the lysosome membrane. The specific structure of this complex allows the protons of hydrogen to be pumped against the concentration gradient , thereby increasing their amount in the internal medium of the organelle.

Hydrolases can only function in an acidic environment. This plays an important protective role, since in the cytoplasm of the cell the medium is practically neutral. If the membrane of the lysosome is damaged in some way, and the enzymes enter the cytosol, they will lose the ability to break down substances and organelles.

The membrane of the lysosome consists of lamellar and micellar regions. The gaps between the phospholipid layers are filled with water. Over the entire area of the membrane are scattered numerous pores, which are also filled with water and can be closed by polar molecules. Such a complex of membrane regions and the pore system makes it possible to penetrate into the organelle both hydrophobic and hydrophilic molecules.

How are lysosomes formed

The proteins necessary for building a lysosome are initially synthesized in ESR. Then they must be "marked" by attaching the mannose residue. This mannose residue is a specific signal for the Golgi apparatus: the proteins concentrate in one place, after which a bubble with lytic enzymes is synthesized from them. That's what lysosomes are in biology.

Internal contents of lysosomes

What is lysosomes and what is the composition of the internal environment of these organelles?

Inside the lysosome, an acidic medium is maintained , the pH of which reaches 4.5-5. Under such conditions, enzymes can fulfill their splitting function. Hydrolases are a common name for a whole class of enzymes. In total, the lysosome contains about 40 different biologically active molecules that catalyze their own, absolutely specific reaction.

The following enzymes can be found in the internal contents of the lysosome:

• Acid phosphatase - cleaves substances containing phosphate groups;
• Nuclease - destroys the nucleic acids ;
• Protease - cleaves proteins;
• Collagenase - destroys collagen molecules;
• Lipase - cleaves esters ;
• Glycosidase - accelerate the reaction of carbohydrate cleavage;
• Asparaginase - cleaves aspartic acid;
• Glutaminase - destroys glutamic acid.

In total, lysosomes contain about 40 different types of hydrolases. Therefore, the question of what is a lysosome, in biology can be answered: a storehouse of enzymes.

Types of lysosomes

There are 4 types of lysosomes: primary and secondary lysosomes, autophagosomes and residual corpuscles.

The formation of lysosomes is a complex process that is accompanied by the operation of various signal molecules on the surface of EPR and AG. The primary lysosome is a small vial that is split off from the membrane by the Golgi apparatus.

The primary lysosome initially contains the entire complex of enzymes necessary for the cleavage of macromolecules.

Secondary lysosome is a structure that is large in volume. It is formed by the fusion of the primary vesicle with substances trapped by endocytosis, or with the products of cell metabolism that must be disposed of.

The formation of autophagosomes is associated with a process such as autophagy - absorption and "digestion" of the spent organelle cells.

The average duration of mitochondria is 10 days. Once the organelle is unable to perform its functions, it must be disposed of. To this end, a number of primary lysosomes surround the mitochondria and are joined together. As a result, an autophagosome of large size is formed, inside which the mitochondrial cleavage begins on monomers.

What is a residual body of lysosomes? This is the final point of the functioning of any lysosome, when the enzymes have performed their work, and in the organelle there are substances that can not undergo further cleavage. Undigested residues are simply thrown out of the cage.

Diseases associated with impaired lysosomal activity

The enzymes do not always work properly. Lysosomes perform the function of cleavage only when the hydrolases have no disturbances in the structure. Therefore, many diseases associated with lysosomes are based on the improper work of enzymes.

Such deviations are called accumulation diseases. This means that if a certain enzyme is deficient, its basic substrate is simply not digested in the lysosome, which is why it accumulates and causes unfavorable consequences.

Sphingolipidosis, Tay-Sachs syndrome, Sendhoff's disease, Nyman-Pick disease, leukodystrophy - all these diseases are associated with abnormal operation of the enzymes of lysosomes or their complete absence. Most diseases are recessive.